Conventional coin-operated mechanisms, such as vending and gambling machines frequently have simplified slug detector mechanisms such as magnetic means to detect slugs made of ferrous material as opposed to coins which are generally made of non-ferrous material, as well as size control means which attempt to distinguish between the different size coins of different denominations. Such mechanisms frequently have coin lock-out mechanisms which either accept or reject coins inserted into the mechanism. For example, with a solenoid-actuated lock-out, an energized solenoid will allow a coin to be accepted, while a de-energized solenoid will reject the coin, so that, by way of illustration, when the machine is unplugged and inoperative, coins are rejected and returned to the customer. In general, however, it has been exceedingly difficult to consistently detect and reject a non-ferrous "slug" which is the same size as the coin denomination intended for the machine.